This invention relates to a process for the preparation of a partially-substituted fluorosilane. More specifically, the present invention is concerned with an improvement in a process for preparing a fluorosilane (e.g., monofluoromonosilane, difluoromonosilane, trifluoromonosilane) by halogen substitution. 2. Description of the Related Art
Partially-substituted fluorosilanes are useful for the formation of thin films of fluorinated amorphous silicon.
Known processes for the preparation of a partially-substituted fluorosilane include the so-called halogen substitution process in which a corresponding chlorosilane is fluorinated with a fluorinating agent.
Use of zinc fluoride (hereinafter referred to as "ZnF.sub.2 ") as the fluorinating agent is disclosed in Japanese Patent Laid-Open No. 151015/1986. Further, this patent publication discloses that all equipments employed in the reaction, to say nothing of ZnF.sub.2, require full drying immediately before their employment because a chlorosilane or fluorosilane undergoes hydrolysis in the presence of water and also that the drying of ZnF.sub.2 can be achieved sufficiently by heating it, for example at 200.degree. C. for 4 hours.
It has however been found that, when halogen substitution of a partially-substituted chlorosilane is carried out using ZnF.sub.2 treated as described above, fluorosilanes other than the corresponding partially-substituted fluorosilane, silanes and silicon tetrafluoride are byproduced.